1. Field of Invention
The present invention relates to a gas generator for a restraining device such as an airbag system for a vehicle.
2. Description of Related Art
In a gas generator, an ignition device is actuated by an ignition current, and a gas generating agent disposed inside a housing is burned, or a pressurized gas charged therein is released, thereby generating gas.
In a pyrotechnic gas generator using a gas generating agent, the pressure is generated inside the housing during the actuation, and therefore the gas generator is designed with a tolerance for the generated pressure in order to prevent the housing from being damaged by the pressure. Accordingly, the parts are strongly joined together in the joint by welding or the like. As a result, air tightness of the joint is ensured and the generated gas does not leak from the joint during the actuation.
However, an equipment for conducting welding in industry is expensive and the number of process steps in the production line increases because the welding step is included. Further, in the case of conducting welding, welding heat is generated, and thermal insulation should be performed or parts should be added to prevent heat transfer to the gas generating agent or explosives located inside the housing.
In addition to welding, crimping is known as another method for fixing the housing. The crimping does not generate a large amount of heat and therefore erroneous ignition of the gas generating agent or explosives by heat is prevented. However, the crimping does not ensure a sufficient joining strength, compared to welding.
Another problem is that the sealing ability of the joint is insufficient.
In an inflator 100 shown in FIG. 1 of U.S. Pat. No. 5,458,371, a housing is formed by a combination of a diffuser cover 104 and an annular base 106.
The diffuser cover 104 is obtained by integrally forming a round top plate 110 and a tubular outer circumferential wall 112having a gas discharge hole 116 formed therein. The annular base 106 is a substantially round disk having an inner circumferential edge 106a and an outer circumferential edge 106b and is formed by complexly bending.
A lower end 112a of the tubular outer circumferential wall 112 is fixed by bending with respect to the annular base 106 (an outer circumferential edge 106b). The inner circumferential edge side of the annular base 106 is fixed by welding 146, but the circumferential edge side is not fixed by welding, as can be also confirmed by comparison with FIG. 2.
The annular base 106 has a substantially round disk shape, but is bent in a complex manner so as to project to the outside of the housing, and the outer circumferential edge 106b that is not fixed by welding is held by the crimped lower end portion 112a. 
U.S. Pat. No. 4,296,084 discloses a gas generator 1 including a housing in which a diffuser housing 10 and a base 12 are joined by screws 18 and 20.
The central portion of the base 12 projects to the inside of the housing, and an adapter 42 having a squib 60 fixed thereto is attached to an opening in the central portion. Meanwhile, the screw 18 is formed in the outer circumferential edge of the base 12, and the base is deformed so as to project toward the outside of the housing at the outer circumferential edge.